The present disclosure generally relates to gas purification systems and processes of use, wherein absorbed ammonia and carbon dioxide are recovered. In particular, the present disclosure relates to wash systems and processes configured to utilize nanofiltration or reverse osmosis to reduce the steam duties of an ammonia recovery stripper for reducing the ammonia slip and other contaminants from a gas stream that has been subjected to an ammonia-based CO2 removal process.
In conventional industrial technologies for gas purification, impurities, such as H2S, CO2 and/or COS are removed from a gas stream such as flue gas, natural gas, syngas or other gas streams by absorption in a liquid solution, e.g., in a liquid solution comprising ammonia and/or one or more amine compounds. The used liquid solution is subsequently regenerated in a regenerator column to release the impurities comprised in the solution, typically by countercurrent contacting with steam. The steam needed for regeneration is typically produced by power plant turbine system. In addition, a reboiler in fluid communication with the regeneration column may provide further release of impurities comprised in the liquid solution.
In current chilled ammonia processes and systems, ammonia slip from the main CO2 absorber is first captured in a water wash vessel and subsequently regenerated in the ammonia recovery stripper by heating the ammoniated rich solution with saturated steam. The ammoniated slip solution typically has a NH3 molarity of 0.1 to 2.0 mol/liter depending on the operating conditions. The current ammonia recovery process from the stripper is an expensive process (approximately 20% heat duty of the main CO2 regenerator) in terms of both capital and operating cost because it is very difficult to integrate stripper overhead heat with the main regenerator network.
Accordingly, there is a need for improved systems and processes for more efficiently recovering the ammonia slip so as to provide reduced energy consumption.